Transcutaneous pins have been known for many years and are used in bone surgery, particularly in external osteosynthesis. Such pins pass through the flesh and bone and, in general, are used with the type of external skeletal fixation appliances developed by Dr. Hoffmann. These external skeletal fixation appliances comprise swivel joints, connecting bars, sliding bars, articulations, and anchorage clamps intended to hold and position the transcutaneous pins. The Hoffmann external fixation devices comprise an assembly framework placed around a part or member of the human body and arranged to hold bones or bone fragments in place from the exterior with the aid of pins or groups of transcutaneous pins.
There are many types of transcutaneous pins on the market today. These pins generally comprise a threaded portion with a tapping portion at the end arranged to cut a thread when it is screwed into a bone part or fragment. Before the pin is installed, the bone or bone fragment is first drilled to the desired diameter, which is substantially equal to or greater than the inner diameter of the thread. The end of the pin is then inserted in the drilled hole and the threaded portion of the pin is screwed into the hole. During this operation, the tap provided at the end of the pin cuts the thread in the previously drilled hole. To screw the pin into the hole, use is commonly made of a chuck engaging a portion of polygonal cross section, for example a square cross section located at one end of the pin. In the pins of the prior art, the end of the threaded portion might take a form like the point of a drilling bit or take different configurations known to those skilled in the art.
There is also a type of pin, known as a transfixing pin, in which the threaded portion is preceded by a rod having a drill tip at its free end. Transfixing pins may be installed without previously drilling a hole in the bone. In the case of a transfixing pin, the hole is drilled by the extremity of the tip and the thread is tapped by a tapping portion provided at the beginning of the thread.
The transcutaneous pins of the prior art do not afford a drilling or a tapping of very high quality. As in any drilling or tapping operation, the temperature rises at the place of the operation, which can cause necroses and deteriorations in the bone tissues. Moreover, the prior art pins do not produce tapped surfaces of good quality. The surfaces are torn out in places, thus failing to provide a good quality of anchorage between the bone fragment and the pin when the latter has been installed. Finally, the prior art pins, by reason of their poor performance in the drilling or tapping operation, can cause undue stresses in the bone when they are in place.